1. Field of the Invention
The present invention relates to an improved process for the production of viscose and also relates to a process for spinning of the viscose thus obtained as well to the respective products, viz. the viscose spinning dope itself and the regenerated cellulose yarn obtained through said processes.
2 Prior Art
In the viscose rayon continuous spinning processes, the viscose spinning dope is extruded through suitable spinnerets into a coagulating bath, is subjected to the coagulation and drawing operation in said bath and in subsequent baths, and then is conveyed to a support and advancing apparatus which causes it to travel in an essentially helical path while the yarn undergoes a succession of treatments until it reaches the desired final characteristics. It is known that said treatments also comprise chemical and/or mechanical treatments intended to eliminate or to reduce to a minimum the sulphur content of the finished products and to bleach the yarn itself. Actually it is known that during the viscose preparation process a xanthation i.e. sulphuration stage of the alkali-cellulose is carried out, in which stage sulphur containing by-products are formed besides the cellulosic ester. Some of said by-products form, during the subsequent treatments, and more precisely, during the contacts with the coagulating bath, elementary sulphur besides carbon sulphide and hydrogen sulphide. The presence of elementary sulphur in the finished fiber causes considerable disadvantages, among them serious drawbacks during the fiber dyeing phase and an increased sensitivity of the finished product to the light.
In particular, the sources of sulphur are on the one hand by-products formed during the xanthation of the alkali-cellulose which contains polysulphide linkages (--S--S--), such as e.g. perthiocarbonates (Na.sub.2 CS.sub.3+x), sodium thiosulphate (Na.sub.2 S.sub.2 O.sub.3) and polysulphides (Na.sub.2 S.sub.x), and on the other hand the hydrogen sulphide, which is generated during the contact with the acid coagulating bath, which also produces sulphur by oxidation. The sulphur produced by the compounds having polysulphide linkages is dispersed in the structure of the fiber and is therefore most difficult to eliminate.
The viscose rayon continuous spinning processes comprise treatments for the elimination or the reduction to a minimum of the sulphur content, which treatments were difficult to carry out since the time that is available for this purpose, e.g. for the contact with the respective chemical treatment agents, especially in high speed spinning, are very short. Further, the need to carry out different chemical treatments in order to impart different desired characteristics to the finished yarn, in zones which are very close to the treatment device, required the use of complicated devices adapted to avoid mixtures or spraying of treatment liquors having different chemical compositions. The resulting apparatus was complicated and expensive and, furthermore involved a high consumption of chemical treatment agents.